Delete temporary tiff file at exit.  Fixes https://bugs.edge.launchpad.net/bookreader/+bug/611077
Delete temporary tiff file at exit.  Fixes https://bugs.edge.launchpad.net/bookreader/+bug/611077

yankl/bookreader,brisandbeans/bookreader,openlibrary/bookreader,gootdude/bookreader,garyrh/bookreader,yankl/bookreader,yankl/bookreader,garyrh/bookreader,yankl/bookreader,Islandora/internet_archive_bookreader,internetarchive/bookreader,Islandora/internet_archive_bookreader,brisandbeans/bookreader,openlibrary/bookreader,internetarchive/bookreader,brisandbeans/bookreader,garyrh/bookreader,niksu/bookreader,Islandora/internet_archive_bookreader,garyrh/bookreader,niksu/bookreader,niksu/bookreader,Islandora/internet_archive_bookreader,brisandbeans/bookreader,nikolas/bookreader,niksu/bookreader,gootdude/bookreader,gootdude/bookreader,garyrh/bookreader,openlibrary/bookreader,nikolas/bookreader,yankl/bookreader,openlibrary/bookreader,brisandbeans/bookreader,gootdude/bookreader,Islandora/internet_archive_bookreader,openlibrary/bookreader,niksu/bookreader